1. Field of the Invention
The present invention relates generally to apparatus for providing a substantially liquid free working environment on a submerged surface, and, because of its ability to conform to underwater surfaces of different shape, it is particularly suitable for, but is not limited to, apparatus for providing substantially liquid free working environments on the submerged surfaces of ships or boats.
2. Description of the Prior Art
Devices for providing substantially liquid free working environments on submerged surfaces are well known in the prior art. For example, caissons and cofferdams have been used for years to provide substantially liquid free working environments on the submerged surfaces of ships, etc. Unfortunately most such caissons and cofferdams do not have the ability to form water tight seals with submerged surfaces of widely varying shape, such as the widely varying shapes which occur at various locations on the hulls of many boats. For example U.S. Pat. No. 808,638 issued to Cunningham displays a caisson for repairing the bottom of floating dry-docks. As is made clear from the disclosure of the Cunningham patent, its caisson is only capable of forming a water tight seal with vessels that have substantially flat bottoms. Thus, the caisson disclosed in the Cunningham patent would be largely useless for the irregularly shaped bottoms of most sailboats and other displacement type vessels.
The prior art has disclosed some devices for providing substantially liquid free working environments on submerged surfaces of varying shape, but none of these prior art devices is sufficiently inexpensive or convenient to have made its use profitable in the performing of underwater repairs or the installation of through-hull fittings in small and medium sized sailboats. For example, U.S. Pat. No. 538,780, issued to Holford discloses a caisson which can be attached to the submerged surface on one side of the hull of a sailboat at various locations along the length of that hull. But the device disclosed in the Holford patent is not very convenient to use, since it requires preformed ribs which have been shaped to fit exactly each portion of the hull to which it can be attached. Furthermore it requires that the caisson be substantially re-built each time it is moved to a different location upon the hull, and it requires that the whole caisson assembly be bolted to the side of the ship.
Another problem found with prior art devices for providing liquid free working environments on submerged surfaces is that they fail to provide means for enabling one located outside of such liquid free environment to perform work within them. Thus if it is desired to perform work in a liquid free environment upon an underwater surface with devices of the prior art it is necessary either to have the caisson or cofferdam large enough to have a person placed within it to perform such work, or, in case of a submerged surface which has liquid on only one of its sides, to make a hole through that portion of the submerged surface which is covered by a cofferdam to enable work to be performed on the covered surface from its dry side through such a hole.
Caissons which are large enough for a human worker to fit within them are, because of their size, expensive and difficult to handle. No convenient means has been found for enabling such large caissons to form liquid tight seals with underwater surfaces of varying shapes. Furthermore, such caissons can be a safety hazard, since if they flood, they can trap and drown a worker caught within them.
Cofferdams can be used to cover a portion of the liquid facing side of an underwater surface which has liquid on only one side to enable work, such as the drilling of holes, to be performed from that surface's dry side. However, the types of work which can be performed on the liquid facing side of submerged surfaces from their dry side is limited. For example, the installation of many through-hull fittings in sailboats cannot be performed solely from the inside of the hull, because the holes in which such through-hull fittings are placed normally have a bevelled edge on the exterior of the hull, making such holes wider on the exterior surface of the hull than on the interior surface. It is very difficult to drill such a bevelled hole from the interior of the hull. Furthermore, through-hull fittings normally have a head on the exterior of the hull that is wider than the smallest diameter of the hole in which it is mounted. Thus it is impossible to install such through-hull fittings from the interior of the hull. As a result, it is presently the practice to pull small and medium sized sailboats out of the water whenever such a through-hull fitting is to be installed.